collect coverage for all class elements for filename

[qododavid]

updates the cobertura coverage report processing logic to process all class elements for each file. This wont make a difference for most languages but Go in particular will have coverage reports with this pattern.

For example, the fragment below shows multiple class tags for the same file.

<classes>
	<class name="-" filename="taskmgr/internal/tasks/store.go" line-rate="1" branch-rate="0" complexity="0">
		<methods>
			<method name="NewFileStore" signature="" line-rate="1" branch-rate="0" complexity="0">
				<lines>
					<line number="23" hits="1"></line>
					<line number="24" hits="1"></line>
					<line number="25" hits="1"></line>
					<line number="26" hits="1"></line>
					<line number="27" hits="1"></line>
				</lines>
			</method>
		</methods>
		<lines>
			<line number="23" hits="1"></line>
			<line number="24" hits="1"></line>
			<line number="25" hits="1"></line>
			<line number="26" hits="1"></line>
			<line number="27" hits="1"></line>
		</lines>
	</class>
	<class name="FileStore" filename="taskmgr/internal/tasks/store.go" line-rate="0.82857144" branch-rate="0" complexity="0">
		<methods>
			<method name="Add" signature="" line-rate="1" branch-rate="0" complexity="0">
				<lines>
					<line number="29" hits="1"></line>
					<line number="30" hits="1"></line>
					<line number="31" hits="1"></line>
					<line number="32" hits="1"></line>
					<line number="33" hits="1"></line>
					<line number="34" hits="1"></line>
					<line number="35" hits="1"></line>
					<line number="36" hits="1"></line>
...